Trailing arm suspensions are widely used in the heavy duty trailer industry for over-the-road trailers and specialty trailers. Those versed in the art are familiar with the competing interests of weight, clearance, ease of installation and cost.
Trailer manufacturers look to the suspension industry to provide affordable suspension systems which can be shipped and installed by the trailer manufacturer. It is highly desirable that the suspension systems may be attached to trailer frame members without substantial customization by the trailer manufacturer. One of the challenges for suspension manufacturers to overcome is to design a suspension assembly for low clearance and specialty trailers that is capable of carrying extremely heavy loads. In particular, low clearance trailers having two or more sets of axles provide a unique and difficult problem because the low clearance necessitates a suspension system that is capable of being mounted in a very small space on a low clearance frame while maintaining adequate wheel travel and overall ground clearance required for practical applications.
Rather than the trailer manufacturer shipping a partially completed frame assembly to the suspension manufacturer for installation of a suspension system, it is highly desirable that the suspension manufacturer create a suspension unit that is mountable to the trailer frame by the trailer manufacturer. This saves substantial shipping costs that would be incurred by moving the trailer frame between the manufacturers.
As will be appreciated by those skilled in the art, one of the more difficult challenges to suspension manufacturers for low clearance trailers is the positioning and placement of air brake actuators. It is critical that a heavy haul low suspension trailer be provided with adequate braking. It is often necessary to install air-actuated disc-type brakes on at least one of the trailer axles to provide the required braking power.
While many disc brake manufacturers recommend mounting the brake actuator directly to a disc brake assembly, suspension manufacturers have developed a variety of devices to mechanically link the air brake actuator to the disc brake assembly while mounting the brake actuator to the suspension remotely from the disc brake assembly. These mechanical links include a variety of push or pull rods, trip levers and similar mechanisms.
Trailing arm suspensions come in two general configurations, overslung or underslung. An overslung trailing arm suspension includes a beam-over-axle orientation while an underslung assembly comprises a beam-under-axle configuration. For low clearance trailers underslung suspension assemblies are preferred because the underslung orientation has lower clearance capabilities.
Trailing arm suspensions can take a variety of shapes and cross sections and can either be formed from cast parts or fabricated from steel plates. Fabrication using steel plates may afford the manufacturer more flexibility in overall suspension design and typically results in lower weight than cast beam assemblies.
One of the basic component parts of a trailing arm suspension is a suspension beam, or control arm, with a connection end for fastening the beam to a trailer frame, the beam body, and axle seat for connecting the axle to the beam and a spring mount for securing a spring assembly between the beam and the vehicle frame.
A variety of methods for connecting a trailing arm suspension beam to a vehicle frame, or chassis, are known within the industry. A common fastening technique is to provide a wishbone end to the trailing arm suspension beam which is fastenable directly to the frame member by placing one arm of the wishbone on either side of the frame. A typical installation would include a bushing through a hole provided in the frame at the point of attachment, and a bolt or similar fastener passing through both arms of the wishbone and the frame bushing. The wishbone attachment method may be preferred for a trailer having multiple sets of axles as it allows the front axle to be moved forward on the frame.
Another common method for attaching a suspension beam to the vehicle frame is a suspension hanger assembly. A suspension hanger is mounted to and depends from the frame. The front portion of the suspension beam, whether cast or formed from plates, is provided with a hole traversing the width of the beam. Usually, a bushing is placed in this hole and then positioned within the hanger. A bolt or similar fastening mechanism secures the beam and associated bushing within the hanger.
The body of the beam itself can be cast or manufactured from plates. For manufactured beams, there are two general types of beam bodies. The first has two side plates, a top and bottom plate to form an open box which has a rectangular cross section. The other common type of manufactured beam is an I-beam having a single vertical plate, a top plate and bottom plate that has an I-shaped cross section. Other configurations of plates may be utilized, and the exact configuration or number of side plates is not limiting of the invention.
The axle seat portion of a suspension hanger beam generally includes a structural member attached to the beam body so that an axle can be mounted perpendicular to the beam. As mentioned above, typical beams are provided in either an underslung or overslung orientation and the axle seat is formed either at the top of the beam, the bottom of the beam or sometimes transversely through the middle of the beam to accommodate the preferred suspension orientation. For the purpose of an underslung beam axle, the axle seat is formed near or at the top plate of the beam and may comprise a C-shaped or arcuate piece of metal that is substantially mateable to the outer periphery of a vehicle axle. The axle is typically welded to the axle seat although it could be clamped or fastened by other known means.
At the second or rearward end of the beam an air spring mounting plate is generally provided. This plate provides a platform onto which the lower most portion of a resilient suspension spring is attached. The uppermost or top portion of the resilient air spring is attached to the vehicle frame or to a plate mounted on the vehicle frame. The resilient air spring contributes to limiting the vertical travel of the suspension beam and cushions or dampens the vertical beam travel. The exact orientation of the air spring mounting plate on the suspension beam is often controlled by the requisite amount of air spring travel for a specific application. One of the difficulties of trailer suspension design is finding a mounting position for the air spring mounting plate on the suspension beam that affords enough wheel travel while still accommodating the desired low trailer clearance.
Because of the compact space for mounting the trailing arm suspension beam on a low clearance trailer, it is extremely difficult and challenging to find a place to mount an air brake actuator for direct connection to a disc brake mounted on the axle spindle. Generally, the actuator cannot be placed between the suspension beam and the trailer frame because it limits or affects vertical wheel travel, effectively becoming a “stop” on the beam, or requires substantial modification to the trailer frame to allow the required travel. It is also less than desirable to mount the air brake actuator below the suspension beam because of ground clearance issues and the likelihood that the brake actuator would become damaged by contacting the road or objects on the road.
A trailing arm suspension beam assembly configured for heavy duty, low clearance trailer applications that accommodates the connection of the air brake actuator directly to the disc brake housing assembly is described herein. The instant invention includes a uniquely configured trailer arm suspension beam for the specific application, use and requirement. The trailing arm assembly is heavy duty, meets the low clearance objective of a low-boy or similar trailer and provides clearance for an air brake actuator to be mounted adjacent the suspension beam directly onto a disc brake housing assembly mounted at or near an axle spindle.